The Addiction Severity Index is a structured clinical interview developed to fill the need for a reliable, valid, and standardized diagnostic-evaluative instrument in the field of alcohol and drug abuse. The ASI may be administered by a technician in 20-30 minutes producing 10-point problem severity ratings in each of six areas commonly affected by addiction. Preliminary analyses of these problem severity ratings on male veteran alcoholics and drug addicts showed them to be highly reliable and valid. Initial correlational analyses using the severity ratings indicated considerable independence between the problem areas suggesting that the treatment problems of patients are not necessarily related to the severity of their chemical abuse. Cluster analyses using these ratings revealed the presence of six subgroups having distinctly different patterns of treatment problems. Six separate studies are planned in four different populations of subjects: (1) a replication of the original reliability studies, (2) test-retest reliability, (3) concurrent validity, which means correlating the ASI subscales with other measures of the same type, (4) predictive validty, to see how well certain important outcome measures are predicted by the ASI including performance measures of the outcomes of the treatments, (5) item analysis of the existing scales and trying out of additional items, (6) a cluster analysis to determine the subtypes of patietns which are identified by the profile of ASI subscales. Finally, we will assemble all of the data presented in the format of norms for VA vs. non-Va, male vs. female, drug- vs. alcohol patients. The authors suggest the potential use of a refined version of the ASI to match patients with treatments, and to promote greater comparability of research findings.